Functional laminates are documents resulting from the lamination of a plurality of layers. In particular they are used as security documents such as smart cards, ID cards, passports, credit cards and the like.
Functional laminates don't refer only to functional cards, but also refer to semi-finished products like prelaminates or inlays, which are used for example for the manufacturing of smart cards equipped with functional components such as chips or chip modules, RFID antennae, switches and the like. They usually comprise a number of layers, wherein the chip module is embedded in at least one of the layers. The layers are usually made of a plastic material such as polyvinylchloride, polycarbonate or polyethylene terephthalate. To finalize the card, outer layers with printed letters, numbers, images and patterns are often added to the inlay in a subsequent lamination process. For the purpose of concision, the terms cards or RFID cards will be use in the rest of this description in place of the generic term of functional laminate, all being equivalent in the frame of the present application.
RFID cards are widely used for providing remote identification data over a wireless radio signal and can be used in a wide variety of applications, such as employee ID badges, electronic passports, transit/toll payment cards, etc.
Generally, an RFID card comprises a laminated card body and a set of embedded electronic components. Typically, the laminated materials in the card body comprise layers of various plastic or thermoplastic material, paper, textiles and adhesive, etc.
Basically, RFID cards are produced in a laminator machine, where larger sheets are laminated together by applying pressure and/or heat. The sheets are generally cut into individual cards further down the manufacturing process.
When the layers are laminated using heat and/or pressure the macromolecules of the plastic material tend to shorten thus causing the plastic material to shrink. Since the chip or chip module itself does not shrink, the material is subjected to mechanical stress eventually leading to a deformation, a cracking or a delaminating of the material or at least residual stress which can result in damage to the functional components and their contacting with conductors, wires or antenna loops or in destruction of the plastic material around the functional components. In the case of RFID cards, wherein a large part of the surface body is occupied by the antenna, the inner tensions can often cause card wrap, distortion and bending. It is therefore necessary to stress relieve the cards by an efficient cooling operation so that the card deformation is reduced.
The most common process for stress relieving RFID cards is to place a pile of cards or uncut card sheets in a stationary freezer unit. The card sheets are manually collected as they exit the laminator machine and placed in the freezer unit for 24 hours at a temperature of about −40° C. The card sheets are thereafter manually collected again and re-inserted into the remaining manufacturing process. Alternatively, the card sheets are cut into individual RFID cards before being placed in the freezer.
From a process standpoint, it is inefficient to handle the card sheets several times with a manual operation. Moreover, the long lead time for the freezing operation causes an increased inventory in the manufacturing pipeline slowing the overall manufacturing efficiency.
Furthermore, the large amount of manual labour required results in a higher frequency of lifting injuries and a production bottle neck.
There are numerous methods for reducing card bending, which present combinations of cooling and pressing operations.
EP 1 291 169 shows an example of a laminator equipped with a cooling plate, which is cooperating with a pressing roller to cool off the laminated cards at the output side of the laminator.
Another similar example is presented in U.S. Pat. No. 5,399,223, where a cooling block is simultaneously holding the cards flat and applying a cooling effect.
A further example is presented in U.S. Pat. No. 6,352,095, where a card straightening device in a laminating machine presses a card between two plates and uses a cold air flow from a fan to cool off the card.
JP 7097117 shows a similar method where the card is being held between plates and cooled off by a fan.